This invention relates to a chamber block for use in a cytocentrifuge adapted to deposit particles suspended in a supernatant onto a deposition surface and, in particular, to a chamber block which is provided with a supernatant withdrawal system that is centrifugal force responsive.
Described in U.S. patent application Ser. No. 496,099, filed on May 19, 1983, is a chamber block for use in a cytocentrifuge which is adapted to sediment particles suspended in a liquid supernatant onto a deposition surface, such as a microscope slide. The chamber block includes an inlet orifice communicating with an inlet channel through which is introduced a sample of particles suspended in the supernatant. The inlet channel in turn communicates with an outlet channel that terminates in an outlet orifice disposed in adjacency to the deposition surface. When exposed to a centrifugal force field particles and supernatant move toward the deposition surface where the particles are sedimented thereon.
To facilitate the removal of excess supernatant the chamber block includes a recess, preferably in the form of a through-bore, that is adapted to receive an absorbent plug. The plug is fabricated, in the preferred instance, from porous polyethylene material. The bore and the plug are both correspondingly tapered over a predetermined portion of their length. When fully received within the bore the tip of the absorbent plug protrudes beyond the chamber block into contacting relationship against the deposition surface. During centrifugation the centrifugal force imposed on the supernatant overcomes the capillary force exerted by the absorbent material of the plug. As the rotor slows, however, the capillary force of the plug becomes dominant, thereby drawing the supernatant away from the deposition surface.
In practice, however, it has been found that while the centrifuge rotor rotates to its operating speed the presence of the absorbant plug in next adjacency to the deposition surface has the effect of prematurely withdrawing both supernatant and cells suspended therein. This is perceived as disadvantageous since it prevents the sedimentation of cells on the surface.
In view of the foregoing it is believed desirable to provide a mechanism which prevents the introduction of the plug into adjacency with the deposition surface until a predetermined operating speed is reached to thereby prevent premature wicking action of the plug.